Harold Bernstein, MD

Professor in Residence

Contact Information

Narrative

My laboratory’s longstanding goal has been to understand mechanisms regulating cell division, and how such processes play a role in cardiovascular biology and disease. To this end our work has focused on four main areas of basic investigation: 1) mechanisms of cell cycle withdrawal during muscle differentiation; 2) cardiac fate determination in myogenic stem cells; 3) the role of cell cycle machinery in cellular hypertrophy, and; 4) the role of RNA processing in regulating cell division and differentiation. In addition, we recently have initiated two new areas of translational and clinical research that apply our understanding of how muscle cells behave to the development of new diagnostic and therapeutic approaches to heart failure: 5) human embryonic stem cell-based therapies for heart failure; and 6) identification of biomarkers of heart failure in patients with congenital heart disease.

1) To study the cell cycle withdrawal program in skeletal and cardiac myocytes, we have developed methods for differentiating rodent and avian myoblasts into myocytes with spontaneous contractile activity, and for establishing and manipulating primary myoblast cultures. Using microarrays, we have identified several regulatory proteins that are differentially expressed in proliferating myoblasts versus post-mitotic myotubes. We have demonstrated that one of these proteins, Stem cell antigen-1 (Sca-1), specifically regulates the proliferation/differentiation transition during skeletal myogenesis. Current efforts in primary myoblasts and mouse models are focused on determining the mechanisms by which Sca-1 specifically controls myoblast proliferation and regulates myogenic precursor cell self-renewal.

2) To examine the regulation of human cardiac fate determination, we are identifying human embryonic stem cells (hESCs) that preferentially differentiate into cardiomyocytes, and developing methods for isolating developmentally-synchronized hESC-derived myocardial precursors. This will facilitate our efforts to determine the contributions of genetic programming and environmental stimuli to subspecialization of human cardiomyocytes into atrial and ventricular myocardium, and conduction tissue.

3) We have demonstrated that hypertrophic stimuli cause a transient burst of Cdk4 activity, remodeling of the retinoblastoma protein complex, and activation of a subset of E2F-1 target genes in murine myoblasts. This has led us to identify a physiological role for both E2F-1-mediated activation and repression of genes involved in cell growth versus division, respectively. Currently, we are investigating the mechanism(s) by which Cip1/Kip1 and INK4 classes of Cdk-inhibitors facilitate this burst of Cdk4 activity, and the role of chromatin remodeling in the hypertrophic response.

4) We cloned human CDC5, demonstrated its functional role in G2/M progression, and identified its association with the RNA spliceosome. Recently, we have reported the role and mechanism of phosphorylation in regulating CDC5 function and its participation in RNA processing.

5) Over the past several years, the identification of heterogeneous populations of muscle stem cells in the heart and bone marrow has generated great enthusiasm for new approaches to muscle repair and regeneration. However, these studies also have exposed the limitations of current strategies. Taking cues from the highly plastic, developing human heart, we are exploring hESC-based therapies for heart failure in collaboration. Using a mouse model of myocardial injury and cell delivery, we are determining the developmental stage at which hESC-derived myocardial cells engraft in vivo, and examining the effects of hESC transplant therapy on cardiac function. In collaboration with other groups at UCSF and UC Berkeley, we also have begun similar experiments in swine to evaluate synthetic matrices for facilitating cell engraftment, as well as the immune response to cell transplant and these matrices.

6) To complement our efforts toward cell-based therapies for heart failure, we also are investigating better ways to monitor heart failure and the response to therapy in children with single ventricle heart disease, the most difficult congenital heart defect to manage. We have initiated a human research protocol to measure the levels of four proteins and six microRNAs found in blood in children with single ventricle compared to children with structurally normal hearts, to determine whether any of these potential biomarkers predict the presence or degree of heart failure in these children. Future efforts will be directed toward using proteomics to establish biomarker arrays for pediatric heart failure.